1. Field
The present invention relates generally to cellular networks. More specifically, the present invention relates to power allocation for power control bits in such networks.
2. Background
Spread spectrum techniques, such as code division multiple access (CDMA) techniques, are used to communicate information over wireless communication systems. For example, CDMA techniques are in wide use for communications between stationary base stations and remote stations (e.g., mobile cellular telephones) in a cellular network. In accordance with CDMA techniques, several streams of information, typically from different sources or sectors, are each encoded or “channelized” using a different code. These codes allow the information to be transmitted over the same frequency band (commonly referred to as a “CDMA channel”). Each such channelized information stream is commonly referred to as a “code channel”.
Increasing demand for wireless data transmission and the expansion of services available via wireless communication technology has led to the development of specific data services such as 1x evolution data only (1xEV-DO), which was based on the High Data Rate (HDR) system. An exemplary 1xEV-DO type system is defined in Telecommunications Industry Association/Electronic Industries Alliance (TIA/EIA)/IS-856 “cdma2000 High Rate Packet Data Air Interface Specification,” which is one of the first 3G systems used for packet data services with forward link peak rates of up to 2.4 Mbps.
In an exemplary 1xEV-DO system, a forward link transmission, which is defined as data transmission from one base station to one remote station, is defined in terms of frames. A frame is further sub-divided into time slots. Each time slot includes at least a forward Medium Access Channel (MAC) and a Forward Traffic Channel (FTC). The MAC is composed of up to 63 code channels, which are orthogonally covered by 64-ary Walsh codes. Each code channel is identified by a MAC index, which has a value between 1 and 63. The MAC indices include a code-division multiplexed reverse activity (RA) channel and up to 59 reverse power control (RPC) channels. For each sector of a cellular network, a unique MAC index is assigned to transmit information to a specific remote station. In the context of 1xEV-DO, the power control bits in the MAC index identifies, for example, the Walsh channel used to spread the corresponding RPC channel. Furthermore, the remote station uses the assigned MAC index to identify transmissions on the FTC, which is a time division multiplexed channel shared by all remote stations communicating with a given sector. A data scheduler in the base station allocates slots to a user specified by the data rate control information in the data rate control (DRC) channel of the reverse link, which is defined as data transmission from the mobile station to one or more base stations.
When transmitting over the forward link in an 1xEV-DO system, the same amount of power is used to transmit each code channel in the CDMA channel. However, since each MAC index is intended for a different remote station, it has been found to be advantageous to vary the power allocated to the MAC index. The conventional power allocation for the MAC index is based on forward link channel state information received from the remote stations. This information is conveyed by the data rate control value fed back via the DRC feedback channel. A higher data rate control value indicates better channel conditions and therefore less allocated power is needed to ensure a predetermined level of reliability on the power control channel. A lower (or erased) data rate control value indicates poorer channel conditions and therefore greater allocated power is needed to ensure the same level of reliability. However, it has been found that, under certain conditions, using the data rate control value received on the DRC feedback channel to allocate power for the transmission of the MAX index can cause allocation of greater amount of power than is necessary for reliable reception at the remote station.
There is therefore a need in the art for appropriately modifying power allocation for transmission of power control bits in the MAC.